The PHILCO Phorum
39-25 Project - Printable Version

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RE: 39-25 Project - klondike98 - 03-23-2014

Joe, thanks for the thoughts.  Some of the rust was just surface rust but where my mouse friends had consistently made their deposits it was pretty well pitted.  I used isopropanol to get the first layer of dirt and crud off followed by some GoJo and then some light wire brushing with a dremel tool to take off most of the surface stuff.  The deeply corroded areas got multiple naval jelly treatments and eventually a heavier duty wire brushing.  I put rustoleum primer on the pitted areas and sanded them down to get them smooth. For the rest of the areas I was trying to use a technique I think Phlogiston recommended of using a grayish paint with some green added to make a "wash" that goes over the areas where the cadmium coating was taken off.  Unfortunately I didn't too too well at it and it looked like crap so I kept going with some rustoleum aluminum. (The fault was my skills, not Russ's approach!!) I did get the wash technique to work pretty well on the dial mounting bracket but I don't happen to have a pic of that yet.  I'm sure I'll get another chance to practice it!  There's always another rusty chassis!

[Image: https://www.dropbox.com/s/d7zdq5g3wd6s2g7/39-25_rust1.jpg?raw=1]
[Image: https://www.dropbox.com/s/u0l6joygir9587k/39-25_rust2.jpg?raw=1]

RE: 39-25 Project - morzh - 03-23-2014

I say it looks great.
Best is the enemy of good'nuff!

RE: 39-25 Project - klondike98 - 03-23-2014

Thanks morzh

RE: 39-25 Project - OldRestorer - 03-23-2014

one day I will be able to dismantle a chassis and then put it back together... correctly! Icon_lol
I'm at the good'nuff stage myself..

very nice

RE: 39-25 Project - klondike98 - 03-25-2014

This isn't quite "electronic" restoration but it does deal with the chassis so...
I took a shot at reproducing the model # stamp that was on the back of the chassis...here's the original:

[Image: https://www.dropbox.com/s/910xiblvmbzvsom/39-25_modelLabel_orig.jpg?raw=1]

and here's the repro...
[Image: https://www.dropbox.com/s/5jq87meyo44jnc4/39-25_modelLabel_new.jpg?raw=1]

I used a transfer technique (there are quite a few once you start looking for them) that uses freezer paper, inkjet printer and Microsoft word.  I recreated the box and fonts in Word, then flipped the image so it would transfer correctly onto the chassis.  I used a technique similar to that used in this blog: http://home-frosting.blogspot.com/2011/08/transfer-using-freezer-paper.html except I cut the freezer paper into a size just a bit larger then the image and taped it to a regular piece of paper (keeping the waxy side exposed.  I then printed the image onto the waxy freezer paper, carefully cut out the image and pressed it onto the chassis.  Its important to burnish the back of the paper with a spoon or hard round object to be sure to transfer as much of the ink as possible.  I should have pressed mine a little harder.  For a first try, I'm pleased.  I'll coat it with a matte clear coat to keep it from rubbing off.

RE: 39-25 Project - Chuck Schwark - 03-25-2014

Was reading this thread about the ink-stamp transfer on model number.
Great idea.

Also saw you had asked earlier about the "2 2" or "22" black stamped on the rear apron.

I'm thinking it would be the assy line number or inspector's number.
Maybe some internal dating code? Second week of second month or similar?

Chuck

RE: 39-25 Project - klondike98 - 03-25-2014

Thanks Chuck. I suspect that if you and Ron aren't sure about the 2-2, no one will know.

RE: 39-25 Project - Tom Hamilton - 03-26-2014

Bob,

That stamp transfer looks really nice, just like the factory.

Tom

RE: 39-25 Project - klondike98 - 07-15-2014

OK..back to working on the chassis.  Am doing the usual paper cap stuffing and rubber wire replacement.  Stuffed the one electrolytic can that was still with the radio.  Pretty straight forward, lots of room.
[Image: https://www.dropbox.com/s/hd7rvvpa8mf1uw0/39-25_30-2332A.jpg?raw=1][Image: https://www.dropbox.com/s/nrfzxu13go1w1ny/39-25_30-2332A_2.jpg?raw=1]

I've made dogbone resistors from molds as well as from bic pens with the wire wrapped around the end but I'd never made the resistors that were in this radio.  Found some tubing at the harware store, cut it to the right length, slid in the new resistor, filled the ends with a little hot glue and finally painted them.  To get the stripe on I put one lead in my electric screwdriver and rotated it while touching the paint brush to it.  Takes a little practice but they come out nice.  The first photo shows the process for a 70 ohm and the second shows the repro 70k ohm above the original.
[Image: https://www.dropbox.com/s/mra6j4lygiv4e9l/39-25_resistor_restore.jpg?raw=1][Image: https://www.dropbox.com/s/e0q8rhm6e6rt404/39-25_resistor_restore2.jpg?raw=1]

RE: 39-25 Project - klondike98 - 07-15-2014

A technical question for you guys.  A previous repair has replaced the #42 280 ohm wire wound resistor (Part No. 33-128431) with a 10 watt 250 ohm resistor.  They also replaced the # 43 70 ohm 1/2 watt resistor with what looks like another 10 watt replacement. Probably OK but it sure is ugly.  I'm replacing the 70 ohm with a correct reproduction.  Any suggestions on what to do with replacing the 280 ohm?  I have a much smaller 5 watt 300 ohm part that would be easier to hide but I'm not sure of what wattage I can actually use.  Anyone have specs on the original part or an assessment of the wattage required?  Thanks!!
[Image: https://www.dropbox.com/s/e7anw9z01323sfj/39-25_schematic.jpg?raw=1]
[Image: https://www.dropbox.com/s/g5tw19ucly5z5y5/39-25_resistor_question.jpg?raw=1]

RE: 39-25 Project - morzh - 07-15-2014

OK,

so the current through your 280 plus 70 is roughly the same as the current through the field coil.

Take the sch document, deduct B+ (SG of 41) fom the table from the 84's K voltage, and divide it by 2000, this is you current.

Use I-square times R to detemine your 280 and 70 dissipation, use comfort factor of two or more to determine ratings.

RE: 39-25 Project - klondike98 - 07-16-2014

Thank you Mike!!
So that would be:
(((310-210)/2000)^2)*280 *2 = 1.4 watts
and similarly 0.35 watts for the 70 ohm resistor.

So the 0.5 watt spec for the 70 makes sense.

[Image: https://www.dropbox.com/s/tey162um7tw6oxu/39-25_voltages.jpg?raw=1]

RE: 39-25 Project - morzh - 07-16-2014

I would go with at least 1W for 70 Ohm to keep it > 2 ratio.

RE: 39-25 Project - klondike98 - 07-16-2014

Thanks! Actually those numbers include the 2x safety factor already.

RE: 39-25 Project - klondike98 - 07-21-2014

OK this puppy is alive again.  Replaced those ugly wirewound resistors, one with a reproduction 70 ohm 1/2 watt and the other with a 300 ohm 5 watt.  Its a lot less visible than the older replacement and I should be able to get a 2 watt replacement that I can make look more original.  Still have one electrolytic tacked in under the chassis since I haven't located the right can to stuff it topside...will keeplooking.

Here's the new look for the resistor replacements:
[Image: https://www.dropbox.com/s/cscnryhz7tgpzsj/39-25_wirewound_replacements.jpg?raw=1]

And the before and after on the entire underside with replaced rubber wire, recap and resistors restored.
[Image: https://www.dropbox.com/s/vqfyha59ifgtbl7/39-25_chassisBOTTOM.jpg?raw=1][Image: https://www.dropbox.com/s/kla09goiqxb46tz/39-25_bottom_restored.jpg?raw=1]

Taking that pushbutton assembly out and putting it back isn't fun.  Does anyone know if the little rubber pieces in the assembly are critical or not...doesn't seem so as its playing without them:
[Image: https://www.dropbox.com/s/iezjbwnnmsuo8is/39-25_pushbutton.jpg?raw=1]

Here's the topside still on the bench before alignment and dial plate replacement.
[Image: https://www.dropbox.com/s/jdw7m3mbd2ok1u8/39-25_restored_beforealignment.jpg?raw=1]